Stem cells are generally classified according to their origin, essentially adult, embryonic or neonatal origin. Since stem cells are capable of differentiating into a broad variety of cell types, they play an important role in the healing and regenerative processes of various tissues and organs. Enhanced efficacy of stem cell engraftment could improve the outcome of clinical transplantations as well as gene therapy protocols, and might be achieved by modulating the ability of stem cells to home to and repopulate the recipient target. Homing of stem cells and the subsequent inhibition of inflammation are critical for acute wound repair (Liang X et al., PLoS One. 2012; 7:e29999; Wu Y et al., Wound Repair Regen. 2007; 15 Suppl 1:S18-26; and Fu X et al., Wound Repair Regen. 2009; 17:185-91), and directional stem cell migration leads to an effective and specific tissue repair (Huang C et al., J Cell Sci. 2004; 117:4619-28). U.S. Pat. No. 7,365,172 provides a peptide derived from a loop or “lollipop” region of transforming growth factor alpha and is biologically active for causing stem cells to proliferate and migrate. U.S. Pat. No. 8,273,756 provides cells and methods for stimulating proliferation and migration of endogenous and exogenous mammalian stem cells in vivo and in vitro. Ras homolog gene family, member A (RhoA) is essential for cell migration to regulate actin cytoskeleton reorganization and activation of extracellular regulated kinase (ERK), p38 in stem cells has been reported to crucial for their directional migration induced by pro-inflammatory cytokines, chemokines or stromal cell-derived factor-1 (Fu X et al., Wound Repair Regen. 2009; 17:185-91; Ryu C H et al., Biochem Biophys Res Commun. 2010; 398:105-10; Liu W et al., Methods Mol Biol., 2011; 750:307-19), all of which lead to a high specificity and therapeutic efficiency of stem cells in wound repair.
Light provides both illumination and thermal energy. Light exposure is physiologically responsible for human homeostasis such as vitamin D synthesis, sleep-wake cycle, and vision. In addition, phototherapy is a standard treatment for skin disorders, neovascular retinopathy, or musculoskeletal disorder, with the uses of appropriate wavelength, intensity and duration of light exposure. It is known in the art that green light emitting diode (LED) irradiation enhances fibroblast growth impaired by high glucose level (Elke M. Vinck et al., Photomedicine and Laser Surgery, Volume 23, Number 2, 2005, pp. 167-171) and promotes the wound healing by inducing HaCat keratinocytes migratory and proliferative mediators (Tomohiro Fushimi et al., Wound Repair and Regeneration, 2012, 20: 226-235). However, HongRan Choi et al., indicate that red LED irradiation can inhibit activation of pro-inflammatory cytokines, mediate the MAPK signaling pathway, and may be clinically useful as an anti-inflammatory tool (HongRan Choi et al., Lasers Med. Sci. (2012), 27:459-467). Recently, red/NIR LED irradiation has been found to promote MSCs growth and enhance their osteogenic differentiation ability (Kim H K et al., Lasers Med. Sci. 2009; 24:214-22; Li W T et al., Photomed Laser Surg. 2010; 28 Suppl 1:S157-65; and Peng F et al., Lasers Med. Sci. 2012; 27:645-53). It has been demonstrated that over-expression of channelrhodopsin-2 (ChR2) in embryonic stem cells successfully differentiates into functional excitatory neuron under blue LED irradiation (Weick J P et al, Stem cells. 2010; 28:2008-16 and Stroh A et al., Stem cells. 2011; 29:78-88).
However, the mechanism(s) of red/NIR or blue LED irradiation regulating stem cell behavior remains elucidative.
There thus exists a need to explore the effect of light in the enhancement of stem cell migration ability which will be valuable for tissue regeneration or transplantation.